Study a natural co-infection case of Largemouth bass ranavirus, Aeromonas vickert, and Aeromonas hydrophila in Micropterus salmoides

The largemouth bass (LMB) is a significant aquaculture species widely cultivated in China. High-density culture has led to an increased susceptibility of LMB to infection by the opportunistic bacterium Aeromonas. This study investigates a case of natural co-infection with the Largemouth bass ranavirus (LMBV), Aeromonas veronii , and Aeromonas hydrophila in Sichuan Province, China. To identify the causative agents of the infection, two bacterial strains were isolated from diseased LMB specimens and identified through 16S rRNA sequencing as Aeromonas vickert and Aeromonas hydrophila , both of which are gram-negative bacteria. The infection of LMBV was confirmed through polymerase chain reaction (PCR) analysis of tissue samples from the infected fish. After two blind passes of the virus fluid, the typical cytopathological effect (CPE) can be observed. Phylogenetic analysis of the virus sequences showed the highest similarity with LMBV isolates (ON418985 and MW630113) from Guangdong Province, China. This study offers important insights into diagnosing mixed infections in LMB and provides a reference for future research.